How many cases of influenza of several days’ illness having about 12,000 leucocytes, a few sticky râles in the chest, but no signs of definite consolidation, have been observed by the clinicians? These cases recover without further change, and the diagnosis is handed in as influenza without a complication being mentioned. In collecting the blood reports from this group the 12,000 cells accordingly must be considered as having occurred in a simple influenza. We hold that this is not a case of uncomplicated epidemic disease. There is undoubted evidence, as is acknowledged by the clinician, of a bronchiolitis; and how many lungs showing a bronchiolitis at autopsy fail to have a broncho-pneumonia? True it may not be demonstrable by our physical examination. This is often the origin of many high counts in what apparently is considered uncomplicated influenza. The blood picture of the pneumonia following the epidemic was more or less constant, although at the same time the features of the count may be quite different. One could roughly divide the results into three groups: (1) leucocytosis, (2) leucopenia, (3) intermediate or normal. Some pneumonias could be followed during their course through all of these classes. Before discussing the white count we can briefly dismiss the other phases of the blood examination by stating that the red blood cells and hæmoglobin presented nothing by the usual examinations which was of special significance, or in any way characteristic. As an example of the group showing a leucocytosis let us follow a patient through an acute influenzal attack, followed by a pneumonia with a subsequent recovery. An initial leucopenia, gradually or suddenly changing into a very moderate leucocytosis (10,000–15,000), was noted at the onset of the pneumonia. During the course of the complication the number of cells in the majority of cases increased, but rarely advanced beyond 20,000. With lysis or crisis the count dropped toward normal, and by the time the lung signs had disappeared the white cells were at the usual number, or very slightly increased. The point which seemed to us to be of importance was that, even although we had a leucocytosis, it was nothing like the count that one would expect for a lobar pneumonia. Of course, there were a few high counts, but looking at the group as a whole they were relatively low. There are a number of variations to this form of blood picture which we might briefly consider. We have observed secondary rises in the leucocyte count concurrent with a new lung involvement. This type was the one so prone to develop into a condition of non-resolution, fibrosis and ultimate death, with a continuous moderately high leucocytosis to the end. Another variation which we learned to fear was the fall of leucocytes to normal or subnormal after a primary rise, when the clinical course of the case in no way indicated a crisis or lysis pending. Seemingly, the longer the primary